1. Field of the Invention
This invention relates to method for fabricating a III-V Group compound semiconductor that inhibits occurrence of surface defects caused by abnormal growth.
2. Background Art
Gallium arsenide (GaAs) not only has a direct transition band structure but is also capable of forming hetero-structures with good lattice-matching property in combination with compound semiconductor materials represented by the general formula AlxGa1-xAs (0≦x<1). GaAs/AlGaAs hetero-structures are therefore frequently adopted in semiconductor lasers and numerous other types of optical semiconductor devices because they are easy to fabricate and excellent in quality.
An optical device such as an LED adopting such a structure, for example, is fabricated by epitaxially growing thin-film layers of AlxGa1-xAs (0≦x<1) on a GaAs substrate to produce a multilayer structure. The process of forming an AlxGa1-xAs multilayer structure involves overlaying a layer of higher Al content on a layer of lower Al content. Moreover, the layer of higher Al content has a relatively large thickness of around 100 nm.
When an AlxGa1-xAs layer of higher Al content is epitaxially grown on an AlxGa1-xAs layer of lower Al content in this manner, the AlxGa1-xAs multilayer structure is prone to internal football-shaped abnormal growth. As such abnormal growth produces a defect that acts as a path of leak current, it adversely affects the electrical properties and/or optical properties of the device. In addition, the effect of such football-shaped abnormal growth extends to the crystal growth surface and degrades its flatness. The resulting surface irregularity spoils the adherence of the various patterning masks to degrade patterning accuracy and degrade the quality of the device.